What is affected by headphone impedance

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    After the interview, the largest number of questions was related to the headphone resistance characteristic. Consider what the characteristic affects and what it eats with. For better assimilation of the material, we will consistently release materials, collect questions and comments, and move on.

    Before we figure out what and how the resistance of the headphones affects, we’ll figure out what kind of overseas bird it is. And we are preparing for the fact that there will already be two formulas from the standard school course in physics. Those. the material is complex and heavy.

    Resistance headphone often referred to as the impedance or total impedance headphone .

    In terms of terms, where resistance means only the active (resistive) part, impedance (impedance) refers to a combination of active and reactive resistance. Remembering the school physics course, we know that reactance refers to capacitance and inductance.

    The final resistance of the headphones depends on what frequency the resistance is measured at. On the boxes, often only resistance is given or, occasionally, the value obtained at a frequency of 1 kHz. Unfortunately, the accompanying parameters are rarely indicated and one can only guess what the impedance value of the headphones really is.

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    If we are talking about dynamic headphones, then the values ​​are in the form of 16, 24, 32 Ohms, etc. they mean the resistance of the speaker inductor only and do not take into account the resistance of the wire, soldering of contacts and plug. In reality, headphone impedance is usually 1-3 ohms higher and varies slightly between the right and left channels. The most bona fide manufacturers honestly indicate that the accuracy of the indicated resistance is 20 or 30% and this is normal (only the marketer vigorously objects to this, no errors on the box can be brought up - the "truth" kills sales).

    Low impedance and high impedance headphones


    Headphones are usually divided into low-impedance and high-impedance. For in-channel and full-size headphones, the separation boundary is different.

    For full-size: low-impedance headphones have a resistance of less than 100 ohms, and high-impedance headphones are above 100 ohms.

    For intra-channel: low-resistance no higher than 32 Ohms, higher than 32 Ohms - high-resistance.

    What kind of impedance do different headphones have?


    In-ear headphones


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    Most in -ear dynamic headphones have a smooth impedance curve and a value of 16, 24 or 32 Ohms do not have deviations for frequencies from 20 to 20 kHz.

    The horizontal graph shows frequencies from 20 Hz to 20 kHz. Vertical - resistance (on a logarithmic scale).

    Full-size dynamic headphones


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    In full-size dynamic headphones, quite often you can find an uneven impedance curve, with local rises in the low-frequency region and a slight rise in the high-frequency region.

    The resistance can be 32 Ohms without taking into account the reactive part (conditionally, this is 0 Hz, measured by any universal multimeter), but in practice it can be twice as high at certain frequencies.

    Unevenness (rises) can indicate both resonances and design features of the emitter in this headphone case. So, when measuring resistance, the frequency and magnitude of the lift can vary greatly depending on whether the headphones are loose on the table or dressed on a mannequin (in this case, the inner space of the headphones is damped).

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    Some dynamic headphones have no noticeable resonance or deviation. Such a line is conditionally ideal, but it is not recommended to select headphones in this way. In pursuit of improving one characteristic, one has to sacrifice another.
    Among the top-class headphones, you can find impedance curves with both minimal deviations and significant ones. If the headphone shows a narrow-band rise (on the graph above it is the Grado GS1000 ), then the amplifier should be selected with a low output impedance for better control of low frequencies (as by the way with the Grado RA1 branded amplifier ).

    Isodynamic (orthodynamic) headphones


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    In addition to dynamic emitters, the isodynamic type of emitter (and its similar type is orthodynamic) is now widely used . These headphones always have a direct impedance line. Isodynamic headphones are now produced: Abyss , Audez'e , HiFiMan, Oppo, Fostex. In Soviet times, there were headphones TDS-5 / m, TDS-7, TDS-15, TDS-16 and TDS-25. Today, for the models TDS-7 and TDS-15, modding is most often done.

    Formally, this is an ideal load for the amplifier, however, in the region of ultra-high frequencies (megahertz and gigahertz) in some models, the resistance decreases and tends to zero. Such perfidy is not visible on the standard schedule, and with some amplifiers this can lead to a poor-quality mode of operation.

    In-ear reinforcement headphones


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    The impedance of in -ear headphones with a reinforcing emitter hardly looks predictable . For single-driver models, there is a common feature - there is always a local rise in the region of the upper middle frequencies (in the region of 1-3 kHz) and in the region of the highest frequencies. Due to the rise in the high-frequency region, most single-driver reinforcing models “sound clean” in the high-frequency region, because the amplifier gives less distortion in this frequency range.

    In the low-frequency region, typically a typical impedance of 8, 16, 24 or 32 ohms. Above 500 Hz, rises begin.
    If a resistance of 100 ohms at 1 kHz is indicated, this does not mean that the headphones are high-impedance, their resistance can be as little as 16 ohms according to the multimeter (in the low frequency range).

    Hybrid and multi-driver headphones


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    It is impossible to predict the impedance curve for multi-driver and hybrid in-ear headphones . The impedance curve can be anything above 500 Hz. The resistance drawdown can easily reach 4 ohms at the declared 100 ohms at 1 kHz.

    General conclusions


    • The resistance in reality will be like on a box , if the headphones: In-channel dynamic or isodynamic
    • The resistance in reality will be like on a box and have unknown rises if the headphones: Dynamic overhead and full-sized
    • Resistance in reality will NOT be like on a box if the headphones: reinforcing or hybrid

    Why actually know all this? Sometimes manufacturers of amplifiers and players indicate which headphone impedance will be compatible and it is useful to focus on this information.

    If you need to find out the real impedance of reinforcing or hybrid headphones, then you can try to search for measurement results on the Internet. Impedance measurement methods usually give a single result and do not depend on software with a stand or a measuring complex.

    What is the impedance of the headphones?


    Headphone sensitivity


    The sensitivity of the headphones is usually reduced to power, which takes into account two characteristics at once: the voltage supplied to the headphones and current. This is a convenient final characteristic for theorists and extremely confusing for practical use by end users.
    For the average consumer, it is logical to imagine that “sensitivity = volume”. With columns, this works because always the value is indicated by the resistance of the speaker in the form of 4 or 8 ohms, and similarly the power of the amplifier is indicated. It is difficult to get confused.

    But if there are only two typical impedances of 4 and 8 Ohms for the speakers and each amplifier has power for two types of resistance, then the headphones have about 11 impedances: 8,16,24,32,64,128,256,320, 608, etc.

    As a result, the consumer picks up headphones with different impedances and naively believes that he can compare something in terms of sensitivity.

    In order for the “sensitivity = volume” connection to be applied to headphones, sensitivity must be expressed in terms of voltage, not power (as Sennheiser does). But most manufacturers do not indicate at all in what units the sensitivity is given.

    That's why everyone “knows” that high-impedance headphones are quiet, and low-impedance headphones are loud. And they naively believe that high-impedance headphones need a “powerful amplifier”, and a lousy smartphone is enough for low-impedance headphones. And although in reality everything is completely wrong, due to extremely unsuccessful terms from GOST and AES standards, separate “concepts” have formed that contradict the laws of physics, but in a common language they accurately describe the result, such as: “High-impedance headphones need a powerful amplifier”. Physically illiterate, but "everything is clear to everyone."

    We will touch on this topic more deeply (carefully, go to the formulas from school, begin to strain the brain!)

    At the output of the amplifier we do not directly control the power at all, but only the voltage level. Depending on the resistance of the headphones, the current level consumed by the headphones is obtained, which in turn determines the final power level.

    This is very important to understand, as without changing the voltage level at the output of the amplifier, we cannot physically separately increase the current level and thereby increase the power level.

    U = I * R , where
    U is the voltage at the output of the amplifier, V
    I is the current strength, A
    R is the resistance of the headphones, Ohm

    W = I * U , where
    W is the power at the output of the amplifier, W
    U is the voltage at the output of the amplifier, V
    I - current strength, A

    If your brains are not boiling from two simple formulas, you can move on.

    An excellent example is the Beyerdynamic DT 770 series headphones with different impedances of 32, 80, 250 and 600 Ohms (some models are discontinued).

    All headphones have a single sensitivity of 96 dB / mW, which means that if we apply exactly 1 mW to the headphones, then the sound pressure level will be 96 dB SPL.

    At 1 mW for different models, we need to apply different ratios of voltage and current:
    Resistance, Ohm3280250600
    Voltage at 1 mW, mV179283500775
    Current at 1 mW, mA5,63,521.3

    Those. A 32 ohm low-resistance model requires the lowest voltage, but the highest current level .

    A high- resistance model, on the contrary, needs the highest voltage, but the lowest current level .

    We return to the fact that at the output of the amplifier we set the voltage level. For smartphones, this is about 200-300 mV. Physically, the volume limit for high-impedance headphones is visible, which makes high-impedance headphones automatically “quiet”. And we actually lack not the “power” of the amplifier, but a trite voltage.

    But if all manufacturers indicated voltage sensitivity, then everything would be very clear:
    Resistance, Ohm3280250600
    Sensitivity, dB / mW96969696
    Sensitivity, dB / V11110710298

    As can be seen from the table, the difference in volume between models with a sensitivity of 96 dB / mW for 32 and 600 Ohms is 13 dB.
    According to the sensitivity to voltage, we see a direct connection with the volume.

    Main conclusions


    • Sensitivity should be looked not at power, but at voltage. This is the only way to match headphones by “volume”
    • The lower the resistance, the higher the sensitivity of the headphones. The higher the resistance, the correspondingly lower the sensitivity.


    And now, when we see that with different resistance from the amplifier, different voltage and current levels are required, we can go to other dependencies that are affected by the resistance of the headphones.

    Player or smartphone runtime


    The higher the resistance of the headphones - the longer the player or smartphone will work without recharging, because high-impedance headphones consume less current (provided that the headphones are listened to at "maximum" regardless of the final actual volume).
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    If you have a quiet smartphone, then there is no real choice in headphones with different impedances, only low-impedance headphones will have sufficient sensitivity.

    However, if your smartphone or player has a “powerful” output (that is, providing a voltage level above 200-300 mV), then you can choose between high-sensitivity low-impedance headphones and less sensitive ones with higher impedance. In this case, with equal output volume, replacing 16 ohms with 32 ohms will reduce current consumption by one third. Against the background of energy consumption by the processor and other microcircuits, a smartphone or player will probably work, of course, not a third longer, but a quarter or a fifth. For example, with the Colorfly C4 Pro player, the operating time varies from 5 to 8 hours (5 hours with the M-Audio IE40 with a strong drawdown in high frequencies and 8 hours with high-impedance headphones).

    For “powerful” players, such as iHiFi or Hidisz, it’s worth picking up headphones with high impedance, and checking the sufficiency of the volume level in the store “without leaving the cash register”. At Soundpal stores, you can listen to everything and try before you buy.

    Returning to graphs with examples of resistance:
    • Single-driver reinforcing headphones in reality have a higher average resistance and with them a smartphone or player can work longer without recharging.
    • Multi-driver headphones may, on the contrary, have lower average impedance and with them a smartphone or player can work less time without recharging.


    Sound quality


    “Everyone knows” that “high-impedance headphones sound better.” But in this case, not the headphones sound better, but the amplifier gives less current and, as a result, less distortion from the side of the amplifier. But this rule is not a dogma, if the amplifier will work with a voltage level exceeding its normal mode, then the source of distortion will be overload not by current, but by voltage.
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    This is the big secret of the quality of single-driver reinforcing headphones (such as Grado GR8 and GR10 , Etymotic models, older Klipsh), where due to the rises in the upper middle and high frequencies, high-quality sound is obtained with those players and phones where there is complete horror with low-impedance dynamic headphones.

    Headphone frequency response


    If the amplifier does not have zero resistance, then the resulting frequency response will vary depending on the impedance curve of both the headphones and the amplifier. We will consider this in detail in one of the next issues, especially since for this it is necessary to consider what is affected by the total output impedance (impedance) of the amplifier.

    How to measure headphone impedance?


    To get a detailed schedule, you need specialized software and a stand. But to find out the value of active resistance (in the region of the lowest frequencies), a budget multimeter is enough, costing from 200 rubles.

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    It is quite normal when buying headphones to check the resistance of the right and left channels, the difference should not exceed 2-3 ohms between the channels in most cases.

    Author Kuznetsov Roman romanrex

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